electrohydrodynamic problem

Hi all,
I'm currently simulating the electromechanical effects of water droplets under both AC and DC voltages. The water droplet is placed between an energized and grounded electrode on an insulating medium. The droplet volume varies from 30uL-100uL and I am a totally new to COMSOL, however I am using electric currents to study the electric effects on the water drop ( i.e. electric field and scalar potentials)

What I would like to know is what physics to use when studying the mechanical/dynamic effects of the water droplet when subjected to an electric field.
And my second problem is how do I go about calculating both electrical and mechanical forces on the droplet. I have already calculated the electric field.
Attached is my file.

Thanks